Human IL-13 is a 17-kDa glycoprotein cloned from activated T cells and is produced by activated T cells of the Th2 lineage, ThO and ThI CD4+ T cells, CD8+ T cells, and several non-T cell populations, such as mast cells. (Zurawski and de Vries, 1994 Immunol Today, 15, 19-26). IL-13 promotes immunoglobulin isotype switching to IgE in human B cells (Punnonen, Aversa et al. 1993 Proc Natl Acad Sci USA 90 3730-4) and suppresses of inflammatory cytokine production in both human and mouse (de Waal Malefyt et al., 1993, J Immunol, 151, 6370-81; Doherty et al., 1993, J Immunol, 151, 7151-60). IL-13 binds to its cell surface receptors, IL-13Rα1 and IL-13Rα2. IL-13Rα1 interacts with IL-13 with a low affinity (KD˜10 nM), followed by recruitment of IL-4R to form the high affinity (KD˜0.4 nM) signaling heterodimeric receptor complex (Aman et al., 1996, J Biol Chem, 271, 29265-70; Hilton et al., 1996, Proc Natl Acad Sci USA, 93, 497-501). The IL-4R/IL-13Rα1 complex is expressed on many cell types such as B cells, monocyte/macrophages, dendritic cells, eosinophils, basophils, fibroblasts, endothelial cells, airway epithelial cells, and airway smooth muscle cells (Graber et al., 1998, Eur J Immunol, 28, 4286-98; Murata et al., 1998, Int Immunol, 10, 1103-10; Akaiwa et al., 2001, Cytokine, 13, 75-84). Ligation of the IL-13Rα1/IL-4R receptor complex results in activation of a variety of signal-transduction pathways including signal transducer and activator of transcription (ST AT6) and the insulin receptor substrate-2 (IRS-2) pathways (Wang et al., 1995, Blood, 86:4218-4227; Takeda et al., 1996, J Immunol, 157, 3220-2). The IL-13Rα2 chain alone has a high affinity (KD˜0.25-0.4 nM) for IL-13, and functions as both a decoy receptor negatively regulating IL-13 binding (Donaldson et al., 1998, J Immunol, 161, 2317-24), and a signaling receptor that induces TGF-β synthesis and fibrosis via AP-I pathway in macrophages and possibly other cell types (Fichtner-Feigl, Strober et al. 2006 Nat Med 12 99-106).
Several studies conducted in preclinical animal models for asthma indicate that IL-13 plays an important role in asthma. These data include resistance to asthma in IL-13 knockout mice as well as inhibition of the asthma phenotype with IL-13 antagonists (soluble IL-13 receptors, anti-IL-13 mAbs, etc.) in various mouse models (Wills-Karp and Chiaramonte, 2003, Curr Opin Pulm Med, 9 21-7; Wills-Karp, 2004, Immunol Rev, 202 175-90). Multiple studies have demonstrated that pharmacologic administration of recombinant IL-13 to the lungs of mice as well as guinea pigs induces airway mucus hyper-secretion, eosinophilia and airway hyperresponsiveness (“AHR”; Grunig et al., 1998, Science, 282, 2261-3; Wills-Karp et al., 1998, Science, 282, 2258-61; Kibe et al., 2003, Am J Respir Crit Care Med, 167, 50-6; Vargaftig and Singer, 2003, Am J Physiol Lung Cell Mol Physiol, 284, L260-9; Vargaftig and Singer, 2003, Am J Respir Cell Mol Biol, 28, 410-9). These effects of IL-13 are reproduced in transgenic mouse systems with either constitutive or inducible expression of IL-13 (Zhu et al., 1999, J Clin Invest, 103, 779-88; Zhu et al., 2001, Am J Respir Crit Care Med, 164, S67-70; Lanone et al., 2002, J Clin Invest, 110:463-474). Chronic transgenic over-expression of IL-13 also induces subepithelial fibrosis and emphysema. Mice deficient in the IL-13 (and IL-4) signaling molecule STAT6 fail to develop allergen-induced AHR and mucus overproduction (Kuperman et al., 2002, Nat Med, 8, 885-9). Studies using soluble IL-13 receptor fusion protein (sIL-13Ra2Fc) have demonstrated the pivotal role of this cytokine in experimental allergen ovalbumin (OVA)-induced airway disease (Grunig et al., 1998, Science, 282, 2261-3; Wills-Karp et al., 1998, Science, 282, 2258-61; Taube et al., 2002, J Immunol, 169, 6482-9). Efficacy of anti-IL-13 treatment was also demonstrated in a chronic model of murine asthma. In addition to exhibiting features of mucus hyper-secretion and AHR, this model of chronic asthma demonstrates several hallmarks of human disease that are lacking in the more acute models. These include eosinophilia of the lung tissue located in inter-epithelial spaces as well as smooth muscle fibrosis as measured by increases in collagen deposition. The chronic asthma model is induced with repeated aerosol challenges with OVA in OVA-sensitized mice 1×/week for a total of 4 weeks. Anti-IL-13 antibody administered for the final 2 weeks of OVA challenges (from day 36 with efficacy readouts assessed on day 53 of study) significantly inhibited AHR, pulmonary inflammation, goblet cell hyperplasia, mucus hypersecretion, and airway fibrosis (Yang et al., 2005, J Pharmacol Exp Ther, 313, 8-15). IL-13 is implicated in the pathogenesis of human asthma as elevated levels of IL-13 mRNA and protein have been detected in lungs of asthmatic patients, which correlate with severity of the disease (Huang et al., 1995, J Immunol, 155, 2688-94). In addition, human IL-3 genetic polymorphisms, which lead to elevated IL-13 levels, have been identified and are associated with asthma and atopy (Heinzmann et al., 2000, Hum Mol Genet, 9, 549-59; Hoerauf et al., 2002, Microbes Infect, 4, 37-42; Vercelli, 2002, Curr Opin Allergy Clin Immunol, 2, 389-93; Heinzmann et al., 2003, J Allergy Clin Immunol, 112, 735-9; Chen et al., 2004, J Allergy Clin Immunol, 114, 553-60; Vladich et al., 2005, J Clin Invest, 115, 747-54), and elevated IL-13 levels have been detected in the lung of asthma patients (Huang et al., 1995, J Immunol, 155, 2688-94; Arima et al., 2002, J Allergy Clin Immunol, 109, 980-7; Berry et al., 2004, J Allergy Clin Immunol, 114, 1106-9). A genetic linkage between IL-13 and asthma has also been demonstrated as individuals with a polymorphism in the IL-13 gene which causes higher plasma IL-13 levels have an increased risk for atopy and asthma (Wills-Karp, 2000, Respir Res, 1, 19-23).
Due to the role of human IL-13 in a variety of human disorders, therapeutic strategies have been designed to inhibit or counteract IL-13 activity. In particular, antibodies that bind to, and neutralize, IL-13 have been sought as a means to inhibit IL-13 activity. However, there exists a need in the art for improved methods of producing and purifying such antibodies for pharmaceutical use. The present invention addresses this need.